The present invention relates to electro-polymerization of films, and more particularly, to methods for selectively depositing films.
The present invention can be more easily understood with reference to an application in which a thick optical film is to be deposited in a predetermined pattern on a surface. Consider a pixelated organic light emitting diode (OLED) display in which the color of light generated by each pixel is determined by a color conversion layer that is deposited between the light emitting portion of the OLED and the viewer. Typically, red, green and blue emitting pixels are deposited adjacent to one another to provide a full color display. The color conversion layer may be constructed from a fluorescent material that converts the light emitted by the OLED to one of the primary colors. Alternatively, in the case of a white light emitting OLED, the color conversion layer may be constructed from a color filter. In either case, a relatively thick layer of material must be deposited at specific locations on the display while leaving the remaining pixels uncovered.
In conventional semiconductor fabrication, this problem is typically solved by masking the pixels that are not to receive the color conversion layer and then depositing the color conversion material in the unmasked areas. The masks are then removed and the process repeated with the next color conversion material until all of the desired color materials have been deposited. For a full color OLED display, this process requires three different masking, deposition, and mask removal steps. In addition, this process is limited to color conversion materials that can withstand the masking and mask removal steps, as the layers that have been deposited in a previous deposition step must be masked and unmasked in subsequent deposition steps.
Electrolytic deposition of organic polymers is known to the art. This type of deposition requires only that the area to be covered be connected to an electrode that can be selectively powered during the deposition step. In many applications, the areas to be covered already include electrodes that can be separately addressed. However, even if separate electrodes must be provided, the process of depositing a transparent electrode is less complex than the masking, deposition, and cleaning steps discussed above. Further, the materials already deposited in an earlier deposition step do not need to be masked when other areas are coated in a subsequent deposition step; hence more fragile materials can be utilized.
For example, U.S. Pat. No. 6,294,245 teaches the deposition of organic polymers that can be constructed from monomers having four coupling sites on each monomer. The process requires the synthesis of precursor polymers that consist of the monomers joined together by two of the sites. The film is then deposited by linking the precursor polymers electrochemically using the remaining sites. The linked precursor polymers must be insoluble in the solvent used in the deposition; whereas, the precursor polymers must be soluble in this solvent. Unfortunately, the range of materials that can be deposited in this manner is limited. Hence, a monomer with the desired optical properties when deposited in the film is not always available at a commercially attractive price. In addition, the thickness of the films generated per unit time is also limiting.
Broadly, it is the object of the present invention to provide an improved method for depositing films via electrochemical polymerization and an improved class of films.
This and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a film and method for making the same. The film includes a plurality of particles having a desired film property that are entrapped in a matrix of linkage polymer molecules. The linkage polymer molecules non-covalently bind to the particles. The linkage polymer molecules are electrochemically polymerizable in a solvent. The particles are insoluble in the solvent. The film is prepared by providing an electrode and a solution of the linkage polymer molecules in which the particles are suspended. An electrical potential is provided between the solution and the electrode in temporal sequence that causes the linkage polymer molecules to polymerize in the vicinity of the electrode thereby entrapping the particles.